Billie Lourd played Leia in The Rise of Skywalker

There are spoilers for Star Wars: The Rise of Skywalker. ILM Visual Effects Supervisor Patrick Tubach revealed the creative process behind the late Carrie Fisher's (General Leia) inclusion in The Rise of Skywalker.

For the scene depicting Leia's Jedi training with Luke Skywalker (Mark Hamill), Billie Lourd stood in for her late mother.

"Billie was playing her mother," Tubach told Yahoo Entertainment. "It was a poignant thing, and something that nobody took lightly – that she was willing to stand in for her mom.

"It felt great for us, too. If you're going to have someone play [Fisher's] part, it's great that it's [Billie] because there are a lot of similarities between them that we were able to draw from."

The filmmakers also used footage from Return of the Jedi for Fisher's younger face, and visual effects supervisor Roger Guyett added: "What you see is what we developed.

"The idea was to provide this great surprise where they take the helmets off, and you see Luke and Leia's younger faces. We scoured outtakes from the original movies, and we took some pieces and then had to try and figure out the technical aspect of putting that shot together."

However, he noted that it was up to Fisher's family – particularly Lourd, who also plays Kaydel Ko Connix in the sequel trilogy – as to whether her likeness will ever be used in a Star Wars movie again.

He added: "When you see her in this movie, it's the live-action element of her face taken from outtakes of either The Force Awakens or The Last Jedi, and then building a digital Carrie around that face.

"She's wearing a new costume, she's got new hair, she's got new jewellery. We didn't want it to feel like we'd simply taken previous shots from previous movies and just edited her in; we wanted her to be unique to this movie, and we wanted her to be integrated into the scenes.

"JJ's principle in pre-production was, 'I want Princess Leia to be played by Carrie Fisher. How do we do this?' That was the integrity that he wanted brought to it, so that he could really put his hand on his heart and say that Princess Leia was always played by Carrie Fisher."

Lourd writes in Time magazine about becoming the keeper of Princess Leia.

Star Wars: The Rise of Skywalker is in cinemas now.